[NFC][documentation] clarify comment in test

test referenced a relative path to a file, but the path was not correct
relative to the project the test is in

Differential Revision: https://reviews.llvm.org/D86368

Author: christetreault-llvm

llvm/test/Analysis/CostModel/AArch64/sve-bitcast.ll

@@ -1,7 +1,7 @@
 ; RUN: opt -mtriple=aarch64-linux-gnu -mattr=+sve -cost-model -analyze < %s 2>%t | FileCheck %s
 ; RUN: FileCheck --check-prefix=WARN --allow-empty %s <%t
 
-; If this check fails please read test/CodeGen/aarch64-sve-intrinsics/README for instructions on how to resolve it.
+; If this check fails please read clang/test/CodeGen/aarch64-sve-intrinsics/README for instructions on how to resolve it.
 ; WARN-NOT: warning
 
 ; CHECK: Found an estimated cost of 0 for instruction:   %b = bitcast <vscale x 2 x double> %a to <vscale x 2 x i64>